The objective of this research proposal is: 1) to evaluate those factors responsible for normal in vivo platelet survival and to determine possible differences in platelets obtained from difference sources with special attention to the use of Latham Bowl platelet pheresis; 2) to investigate those factors that will permit platelets to maintain energy and to function in-vivo after storage. Time, plasma anticoagulant, oxygen availability and storage temperature will be evaluated for their effect on platelet ATP levels and metabolic activity in vitro, especially in relation to activity of the Kreb's citric acid cycle. The relation between platelet function in vitro and survival of platelets post transfusion will be used to determine factors essential for more efficient platelet storage. In vitro studies will be performed to determine the relationship between serotonin uptake of stored platelets and in-vivo effectiveness. A standardized anti-platelet agglutination test is being devised to provide a reliable measure for the detection of platelet isoantibodies. Thus a realistic evaluation of platelet transfusion therapy in severely thrombocytopenic leukemic patients and the determination of factors and mechanisms that influence these benefits will be possible; 3) the study of the metabolism of leukemic platelets.